Image forming apparatus and method for controlling the same to compensate for registration errors

Abstract

An image forming apparatus may include one or more photosensitive media, a driving unit to rotate the photosensitive media, a detecting unit to detect a rotational state of each of the photosensitive media and a controller to control the driving unit based on the rotational state detected by the detecting unit so that two adjacent photosensitive media stop with a phase angle difference between them that is capable of compensating for image registration errors.

What is claimed is: 
     
       1. An image forming apparatus, comprising:
 a plurality of photosensitive media; 
 a driving unit configured to rotate the plurality of photosensitive media; 
 a detecting unit configured to detect a rotational state of each of the plurality of photosensitive media; and 
 a controller configured to control the driving unit based on the rotational state of each of the plurality of photosensitive media detected by the detecting unit, the controller being configured to control the driving member in such a manner that two adjacent ones of the plurality of photosensitive media stop with a phase angle difference therebetween, the phase angle difference satisfying a formula: 
 
       
         
           
             
               θ 
               = 
               
                 q 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   
                     360 
                     ⁢ 
                     
                       ( 
                       
                         L 
                         - 
                         
                           π 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           D 
                         
                       
                       ) 
                     
                   
                   
                     π 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     D 
                   
                 
               
             
           
         
         wherein θ is the phase angle difference between the two adjacent photosensitive media, L being the distance between the two adjacent ones of the plurality of photosensitive media, D being the diameter of at least one of the plurality of photosensitive media, and q being an integer that represents an ordered position respectively of the remaining ones of the plurality of photosensitive media in an order from closest to furthest from the first one of the plurality of photosensitive media, 
         wherein the detecting unit comprises a reference member disposed on each of the plurality of photosensitive media, the reference member having an arc shape and having a length that is sufficient for detection of the rotational angle of the photosensitive media of 170 degrees, and 
         wherein the reference member disposed on each of the plurality of photosensitive media corresponding to a start point of a same imperfection on each of the plurality of photosensitive media. 
       
     
     
       2. The image forming apparatus of  claim 1 , wherein the plurality of photosensitive media comprises four photosensitive media arranged consecutively along an image transfer path, and
 wherein the controller is configured to control the driving unit so that three photosensitive media located downstream of a first photosensitive medium in the image transfer path stops with the phase angle of θ, 2θ and 3θ, respectively, with respect to the first photosensitive medium. 
 
     
     
       3. The image forming apparatus of  claim 1 , wherein the detecting unit further comprises a detecting sensor configured to detect the reference member. 
     
     
       4. The image forming apparatus of  claim 3 , wherein the reference member comprises a projecting portion formed at a side surface of the photosensitive medium, the projecting portion having an arc shape. 
     
     
       5. The image forming apparatus of  claim 3 , wherein the reference member is formed integrally with the photosensitive medium. 
     
     
       6. The image forming apparatus of  claim 1 , further comprising:
 a transfer mediating belt onto which an image formed on each of the plurality of photosensitive media is transferred; 
 a belt driving roller configured to rotate the transfer mediating belt along a continuous loop. 
 
     
     
       7. The image forming apparatus of  claim 6 , wherein the distance between the two adjacent ones of the plurality of photosensitive media satisfies a relationship,
     L=nπd,    
 wherein L is the distance between the two adjacent ones of the plurality of photosensitive media, d being the diameter of the belt driving roller, n being an integer. 
 
     
     
       8. The image forming apparatus of  claim 6 , wherein the transfer mediating belt comprises one of an intermediate transfer belt onto which respective images on the plurality of photosensitive media are transferred and a printing medium conveying belt configured to convey a printing medium to each of the plurality of photosensitive media. 
     
     
       9. The image forming apparatus of  claim 1 , wherein the controller is configured to control the driving unit so that the two adjacent ones of the plurality of photosensitive media stop with the phase angle difference during a preparation for a printing operation. 
     
     
       10. A method of controlling an image forming apparatus, comprising:
 determining whether to stop rotations of a plurality of photosensitive media; 
 determining a rotational state of each of the photosensitive media if it is determined that the plurality of photosensitive media is to be stopped; and 
 stopping the rotations of the plurality of photosensitive media so that each of the plurality of photosensitive media has a phase angle difference with respect to a first photosensitive medium located upstream of other ones of the plurality of photosensitive media, the phase angle difference satisfying a relationship defined by: 
 
       
         
           
             
               
                 θ 
                 = 
                 
                   q 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     
                       360 
                       ⁢ 
                       
                         ( 
                         
                           L 
                           - 
                           
                             π 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             D 
                           
                         
                         ) 
                       
                     
                     
                       π 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       D 
                     
                   
                 
               
               , 
             
           
         
         wherein θ is the phase angle difference between two adjacent ones of the plurality of photosensitive media, L being the distance between the two adjacent ones of the plurality of photosensitive media, D being the diameter of a photosensitive medium, and q being an integer that represents an ordered position respectively of the remaining ones of the plurality of photosensitive media in an order from closest to furthest from the first one of the plurality of photosensitive media, 
         wherein each of the plurality of photosensitive media comprises a reference member having an arc shape and having a length that is sufficient for detection of the rotational angle of the photosensitive media of 170 degrees, and 
         wherein the reference member disposed on each of the plurality of photosensitive media corresponding to a start point of a same imperfection on each of the plurality of photosensitive media. 
       
     
     
       11. The method of  claim 10 , wherein the plurality of photosensitive media comprises four photosensitive media arranged consecutively along an image transfer path, and
 wherein stopping the rotations of the plurality of photosensitive media comprises stopping the rotations so that three photosensitive media located downstream of a first photosensitive medium in the image transfer path stops with the phase angle of θ, 2θ and 3θ, respectively, with respect to the first photosensitive medium. 
 
     
     
       12. The method of  claim 10 , wherein the reference member for each of the plurality of photosensitive media comprising a projection having an arc shape and projecting from a side surface of the photosensitive medium. 
     
     
       13. The method of  claim 12 , wherein stopping the rotations of the plurality of photosensitive media comprises:
 stopping a first one of the plurality of photosensitive media upon detection of a leading end of the reference member of the first one of the plurality of photosensitive media; and 
 stopping each of other ones of the plurality of photosensitive media after elapse of a time duration after detection of a leading end of the reference member of that photosensitive medium, the photosensitive medium rotating by a rotational distance corresponding to the phase angle difference during the time duration. 
 
     
     
       14. An image forming apparatus having a plurality of photosensitive media arranged consecutively along an image transfer path, each of the plurality of photosensitive media being rotatable and being configured to come into contact with an image transfer medium in such a manner that the image transfer medium receives an image from each of the plurality of photosensitive media, the image forming apparatus comprising:
 a plurality of reference marks each arranged on a respective corresponding one of the plurality of photosensitive media; and 
 a controller configured to control rotations of the plurality of photosensitive media in such a manner that the plurality of photosensitive media stop rotating at respective positions at which each of the plurality of reference marks has a predetermined angular phase difference with an adjacent one of the plurality of reference marks corresponding to an immediately adjacent one of the plurality of photosensitive media, 
 wherein an angular phase difference between a first reference mark associated with a first one of the plurality of photosensitive media located most upstream with respect to a direction of movement of the image transfer medium and each of reference marks associated with remaining ones of the plurality of photosensitive media satisfies a relationship defined by: 
 
       
         
           
             
               
                 θ 
                 = 
                 
                   q 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     
                       360 
                       ⁢ 
                       
                         ( 
                         
                           L 
                           - 
                           
                             π 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             D 
                           
                         
                         ) 
                       
                     
                     
                       π 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       D 
                     
                   
                 
               
               , 
             
           
         
         wherein θ is the predetermined angular phase difference between any two adjacent ones of the plurality of photosensitive media, L being a distance between two adjacent ones of the plurality of photosensitive media, D being a diameter of a photosensitive medium, q is an integer that represents an ordered position respectively of the remaining ones of the plurality of photosensitive media in an order from closest to furthest from the first one of the plurality of photosensitive media, 
         wherein each of the plurality of reference marks has an arc shape and having a length that is sufficient for detection of the rotational angle of the photosensitive media of 170 degrees, and 
         wherein the reference member disposed on each of the plurality of photosensitive media corresponding to a start point of a same imperfection on each of the plurality of photosensitive media. 
       
     
     
       15. The image forming apparatus of  claim 14 , wherein the image transfer medium comprises a sheet of paper. 
     
     
       16. The image forming apparatus of  claim 14 , wherein the image transfer medium comprises an intermediate transfer belt arranged to rotate about a continuous loop in contact with each of the plurality of photosensitive media, the intermediate transfer belt being supported on, and thereby receiving a rotational force, from a belt driving roller. 
     
     
       17. The image forming apparatus of  claim 16 , wherein a distance between two adjacent ones of the plurality of photosensitive media satisfies a relationship defined by:
     L=nπd,    
 wherein L is the distance between the two adjacent ones of the plurality of photosensitive media, d being the diameter of the belt driving roller, n being an integer. 
 
     
     
       18. The image forming apparatus of  claim 14 , wherein each of the plurality of photosensitive media having substantially a cylindrical roller shape with its length extending parallel to a rotational axis about which the photosensitive medium rotates, and
 wherein each of the plurality of reference marks comprises a projection protruding from a surface of an axial end of associated photosensitive medium, the projection defining an arc over a portion of the surface of the axial end. 
 
     
     
       19. The image forming apparatus of  claim 18 , the arc defined by any of the plurality of reference marks being substantially concentric with a circumference of the corresponding one of the plurality of photosensitive media.